Stepping up from welterweight to challenge one of the greatest middleweights in history, he did his reputation little harm but, as expected, was gradually out-boxed and over-powered by the defending champion.

His pursuit of Golovkin's IBF and WBC titles - the WBA chose not to sanction theirs - concluded in the fifth when, struggling to resist the champion's latest powerful assault, Brook's corner threw in the towel.

Referee Marlon Wright responded by waving the action over, and while the crowd booed and Brook complained, he was swiftly tiring and it appeared the right decision.

The 30-year-old's finest chance of victory came in relying on his greatest strengths - his impressive punch accuracy and exceptional timing - and hoping he retained his natural power at the bigger weight.

Golovkin has been known to allow his opponents to land unnecessary punches but on this occasion it was Brook's guts and class that created the moments where he enjoyed success.

The champion's masterful footwork - Brook's lateral and head movement proved limited - also repeatedly forced the Briton to where Golovkin wanted him, setting up the lethal attacks that gradually wore his tough challenger down.

The opening 90 seconds of the fight demonstrated the size of the task he was facing. Powerful hooks to both head and body clearly hurt Brook, threatening an early finish and forcing him to cling on.

He impressed, however, in ending the round in the ascendency and going toe-to-toe with a fighter described as the 'new Mike Tyson'.

He remained the aggressor throughout the second, and much of the third, slowing Golovkin with strong combinations and a powerful uppercut. Even if he out-worked the champion, however, the suspicion remained he was the one being worn down whenever Golovkin landed.

By the start of the fourth a cut by Brook's right eye was beginning to swell, and even with him continuing to time both jabs and counters, the undefeated champion appeared no closer to suffering his first ever knockdown.

The Briton was tired by the start of the fifth, and while he impressively remained on his feet he was gradually offering less in response. With Brook again caught on the ropes and receiving Golovkin's latest powerful combination, trainer Dominic Ingle moved to end the fight.

If Brook's toughness meant he could have continued for at least a little longer, he increasingly appeared the smaller of the two and fighting on could potentially have shortened his career.

The defeat was the first of his otherwise impressive professional record. Stepping up from the welterweight limit that was such a struggle for him means it is likely he will return at light-middleweight, but only the harshest critic would question him losing to a great like Golovkin.